The quality of a structure, whether it is a house, apartment building, or commercial building, is inextricably tied to its foundation. If the structure is not built on a proper foundation, the rest of the structure, even if properly constructed, is likely to show defects over time. When foundations are constructed directly on ground soils, it often creates an unstable environment for the foundation. In addition, if these soils are active or expansive, the environment may be especially problematic. For example, in regions where the soil has a high percentage of active clay, expansion and contraction of the clay subjects the foundations to significant loads (e.g., forces) and potential movement.
Structures built on soils in certain regions may have had their slab foundations and walls displaced and damaged (e.g., cracked foundations and walls) as a result of differential expansion and/or contraction of the soil. Over time, engineers have developed systems and methods for designing foundations in an attempt to minimize damage due to soil movement. Some of these systems and methods include isolating heavy slab foundations from the active soils by suspending the slab above the ground using structural supports (e.g., helical piers, drilled shaft piers, pressed concrete or steel pilings, spread footings, natural rock, etc.) and lifting assemblies (e.g., lifting bolts, hydraulic jacks, air-inflatable jacks, electrical scissor jacks, etc.). For example, U.S. Pat. No. 7,823,341, HEIGHT-ADJUSTABLE, STRUCTURALLY SUSPENDED SLABS FOR A STRUCTURAL FOUNDATION, issued on Nov. 2, 2010, which is incorporated by reference herein, discloses a method of lifting a slab foundation using structural supports and lifting assemblies. The installation of supports and lifts to raise the slab foundation creates a protective void between the soil and the slab foundation, such as may permit the vertical expansion of the soil without subjecting the slab foundation to varying forces associated with the dynamic nature of soil.
Many existing systems and methods for lifting slab foundations after their formation on the ground surface use linear actuators (e.g., hydraulic, pneumatic, etc.) to raise a formed slab foundation. The exterior housing of the actuator is often secured to the slab foundation while a ram (e.g., rod, shaft, etc.) extends out from the actuator to engage a subjacent structural support. Activating (e.g., hydraulically, pneumatically, etc.) the actuator causes the ram to apply a direct pushing force along an axis of intended lifting against the subjacent structural support. As the subjacent structural support is often statically embedded in the ground surface, the pushing force is transferred into a lifting force against the exterior housing of the actuator and the slab foundation in which the exterior housing is engaged, thereby raising the slab foundation above the ground surface.
However, conventional hydraulic and pneumatic lifting assemblies are typically designed for temporary and/or semi-permanent lifting. Accordingly, they not designed to sustain continual downward forces (e.g., gravitational) related to the weight of a lifted slab foundation and a structure and/or occupants thereupon. Conventional pneumatic and hydraulic actuators often fail if not properly maintained or if subjected to repeated use and/or stressful environments (e.g., operating over extreme stress, parts corrosion, seal leakage, etc.). Actuator failures may cause the slab foundation to sink over time or, in extreme situations, collapse. Further, since lifting assemblies are typically displaced underneath a lifted slab foundation and may be difficult to access for maintenance and/or repairs, these actuator failures are difficult to mitigate.